Gypsum

Gypsum is a mineral composed of hydrated calcium sulfate, with the chemical formula CaSO₄-2H₂O. It is formed mainly by water evaporation in shallow marine environments and is widespread in evaporitic sediments. Gypsum is known for its high transparency and softness, with a hardness of 2 on the Mohs scale, making it one of the softest minerals.

It crystallizes in the monoclinic system and can take various forms, such as tabular crystals, sand roses, or fibrous masses like the Selenite variety. Gypsum is appreciated for its use in plaster manufacture, but also by collectors for its clear crystals and attractive shapes.